Pages

Monday, June 5, 2017

I have been sheathing the decks recently. The horizontal surfaces get the worst punishment and I wanted to protect them. I bought two big bolts of stretchy synthetic cloth at the local Memorial Day Flea Market for a few bucks and proceded to roll them out on the decks.

I found little splinters trying to rise up and push up little bubbles under the cloth, so I started wetting the plywood, rubbing a cloth over it against the grain to grab the splinters and lift them, then sanding again to cut them off.

I wetted the whole thing down with water and spread the titebond III, then spread it around with what we used to call a "weenie-roller" in my days on the paint crew.

Now, this business of wetting down with water seemed rather foolish to me at first. I have imported the passage from Dave Zeiger's blog.

Application of Fabric plus Water-Based Pucky

Application consists of the following steps:

Sweep and wet-tack for a dust-free deck

Lay out fabric (may be overlapped, but abutting is sufficient and smoother)

Wet out fabric (Yep. Water... drippy wet)

Paint on pucky (may thin somewhat with water, if necessary for low-drag)

Dry

If not satisfied, repeat from 3 (a bit of weave left provides texture)

Prime and top-coat

The first round of 1-4 is the primary adhesion step. As the water dries out of the weave, waterbourne pucky wicks (is drawn by capillary action) down into pores of the plywood substrate, creating a permeating bond interface. Subsequent layers build to coat and fill the weave.

On a warm, dry day, water evaporates quickly. If the fabric is drying ahead of you, consider keeping a water-brush on hand to refresh the wet. Without that water, wicking is reduced, and glue may not dilute and penetrate the fabric or wood surfaces for full adhesion.

At the end of the first pass, the fabric is only lightly bonded, however, and can be fairly easily torn away. It is reenforced by subsequent passes, however, and the result is firmly attached.

Consider whether to leave some weave for texture (thin matrix), or fill past the top of the weave for longevity (thick matrix). In the latter case, you might consider added texture in the topcoat.

My only semi-eddicated opinion is that green (not completely cured) layers bond better. Thus many layers can be applied in a single day. I especially like to prime over a green layer, in effect gluing the primer to the matrix. The whole seems to cure well over ensuing days (possibly even faster than the generally indicated 24 to 48 hours).

I mean, how can wet wood bond better to glue than dry wood? If there were some great adhesion advantage, wouldn't they tell you to wet the wood whenever you tried to glue it?

Regardless, I found the wetting to really help in positioning the cloth and make everything go smoothly. I can't imagine trying to do it on a hot day with everything dry.

I am looking for something to seal the windows with. Being 7 feet long, they are going to expand and contract with temperature. From what I can determine, we are looking at 1/4"- about 1/8" either direction at the ends, where the expansion and contraction is greatest. I was turned on to "Big Stretch" as a possibility, and I wanted to test it to see.

It claimed a two week setup time, so I made this test piece....

Had I-gor sand it well...

And set up this testing scheme, letting it dry for a month.

I put this goal, 1/4" of one-direction movement, which is twice what it should theoretically have to endure. I put a nut on that little black carriage bolt and started cranking....

The pressure was too much for a little hole in 1/8" acrylic. New approach.

Now we are pushing rather than pulling. You can see the new goal drawn on the plywood.

Here at almost 1/4" past the goal, it looks stressed, but not coming loose.

Another 1/8" and it finally ruptured.

You can see here that it stuck very well to the wood, but not as well to the super-slick acrylic. It could bear some roughing-up with some 220-grit, perhaps.